I first read someone saying something like that here on Free Republic about 15 years ago. It was pretty blunt, and sort of rubbed me the wrong way (having been raised Catholic), so I went and investigated the claim. Over many years.
And it turns out that it's correct. It's interesting, if you take "Votes GOP" as a proxy for "Is Conservative" - then you can measure that. Voting GOP is an indicator that perhaps the person understands the intent of the Founders of the Republic. (So is support for an armed citizenry in my experience). What you discover, if you go look at voting patterns, is that you see that the GOP (and therefore the real American Republic) really is a WASP program, and not too many other groups have signed on to support it, even those who have done very well in America.
I believe Trump carried the non-Hispanic Catholic vote in the last election, but that was a first. Maybe, about 100 years after the high water of Irish and Italian immigration these groups are turning into Constitution supporting Conservatives. That's 5 generations, though, and it's still a lot lower level than people who self-identify as "Evangelical".
I am Catholic, too. I know of what I speak.
Any questions?
Continuing to pretend that American elections can be won with appeals to ideology (or even economics) is a risky game, akin to playing Russian Roulette with our nation. There is no example of a campaign that has moved the needle on the racial voting patterns in the above graph.
George Bush's "Kinder Gentler" Conservatism still lost the black vote, the Jewish vote, the Hispanic vote and the Asian vote to the Democrat. So did Romney, so did McCain. So did Trump.